This set of Class 12 Biology Chapter 5 Multiple Choice Questions & Answers (MCQs) focuses on “Inheritance of Two Genes-1”.
1. In order to study the inheritance of two genes, the parents should be true-breeding for _______
a) a single contrasting characters
b) a pair of contrasting characters
c) a pair of chromosomes
d) a single chromosome
Explanation: With the plants that are true-breeding for two contrasting characters, Mendel performed crosses. Based on these, he devised results for the inheritance of two genes.
2. If round seed (RR) was dominant over wrinkled seed (rr) in a monohybrid cross, and yellow pod (YY) was dominant over brown pod (yy), what should be the starting genotype of parents in a dihybrid cross?
a) RRrr and YYyy
b) RRYY and rryy
c) RRyy and YYrr
d) RrYy and RrYy
Explanation: The dihybrid cross is used to the inheritance pattern of two contrasting characters. Hence, they should be true-breeding. One for both dominant traits and the other for both recessive traits.
3. What is the expected phenotype of F1 progeny of a dihybrid cross for inflated green pod plants and constricted yellow pod plants?
a) Inflated green pods
b) Inflated yellow pods
c) Constricted green pods
d) Constricted yellow pods
Explanation: The F1 progeny will be heterozygotes. Hence the dominant characters will be expressed. Thus, all the F1 progeny will have inflated green pods.
4. Given the genotype of parents as AABB and aabb, what is the expected genotype of F1 progeny?
Explanation: AABB parent will only be able to produce AB gametes, and aabb parent will only be able to produce ab gametes. Thus, the only possible genotype for the progeny is AaBb, a heterozygote.
5. What is the zygosity of the F1 progeny of a dihybrid cross?
Explanation: The F1 progeny of a dihybrid cross are formed by a cross between parents that are homozygous for two traits. Thus, they are all heterozygous.
6. All the progeny of F1 generation of a dihybrid cross are genotypically identical for the locus under study.
Explanation: The dihybrid cross initiates with true-breeding parents who are homozygous for two traits. Thus, each of them can only produce a single type of gamete. Hence the offsprings in the F1 generation are all genetically identical.
7. What is the expected phenotype of F1 generation obtained by the cross between true-breeding round yellow seed plants and true-breeding wrinkled green seed plants?
a) Round green seeds
b) Round yellow seeds
c) Wrinkled green seeds
d) Wrinkled yellow seeds
Explanation: Round seeds are dominant over wrinkled seeds. Also, yellow seeds are dominant over the green seeds. Thus, the progeny of these parents will be heterozygotic resulting expression of only the dominant characters.
8. Which of the following phenotypes is not obtained in the F2 generation?
a) Round yellow seeds
b) Wrinkled green seeds
c) Wrinkled round seeds
d) Round green seeds
Explanation: In the F2 generation of a dihybrid cross, all possible phenotypes are observed. Wrinkled and round are encoded by the same locus. Hence, they cannot occur together.
9. For the cross of round green and wrinkled yellow seeds, which of the following is incorrect with regards to the F2 generation?
a) Round seeds were three times more abundant than yellow seeds
b) Green seeds were three times less abundant than wrinkled seeds
c) Round seeds were as abundant as the green seeds
d) Yellow seeds were three times more abundant than green seeds
Explanation: The roundness and greenness of the seeds are encoded by different genes. According to the law of independent assortment, these two should segregate independently of each other. Thus in the F2 generation, green seeds: yellow seeds = 3:1, round seeds: wrinkled seeds = 3:1. From this, we can have, green seeds: wrinkled seeds = 3:1, green seeds: round seeds = 1:1, yellow seeds: round seeds = 1:3, yellow seeds: wrinkled seeds = 1:1.
10. A cross involving variation in two different traits is called _______
a) monohybrid cross
b) dihybrid cross
c) bihybrid cross
d) polyhybrid cross
Explanation: A dihybrid cross is the one where the partners involved are similar except for two traits under consideration. These were studied for the first time using true-breeding lines by Mendel.
11. The dihybrid cross was used by Mendel to derive the law of dominance.
Explanation: Mendel used the monohybrid cross to arrive at the laws of dominance and segregation. For the law of independent assortment, he did the dihybrid crosses.
12. For the cross of axial violet and terminal white flowers, which of the following is incorrect with regards to the F2 generation?
a) Axial violet are nine times more abundant than white flowers
b) Axial white flowers are as abundant as terminal violet flowers
c) Terminal white flowers are thrice abundant than the axial white flowers
d) Terminal violet flowers are three times more abundant than terminal white flowers
Explanation: This is a dihybrid cross. The genetics is Mendelian since the traits are present on different chromosomes and do not exhibit linkage. Thus, the expected phenotypic ratio is 9 axial violet: 3 axial white: 3 terminal violet: 1 terminal white. Hence axial violet flowers are nine times more abundant than white flowers; axial white flowers are as abundant as terminal violet flowers; terminal white flowers are 1/3rd as abundant as axial white flowers and terminal violet flowers are thrice abundant than terminal white flowers.
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